1. Field of Invention
This invention relates to battery power systems and more particularly to apparatus, methods, media and signals for controlling energy transfer between an energy bus and a system of batteries.
2. Description of Related Art
With the increasing interest in electric vehicles, hybrid electric vehicles and use of battery back-up systems, the need for battery power systems is similarly increasing. Many applications require the use of a series string of rechargeable batteries. The ability of any individual battery in such a string to accept a load or to accept a charge current depends on the individual battery. Various factors affect the ability of a battery to receive or deliver charge and such factors may include operating conditions of the battery such as temperature and state of charge, for example. Other factors such as storage time, float voltage, float life, minimum voltage, number of cycles, depth of discharge and capacity also play a role. Consequently, the operating conditions of each individual battery affect the ability of the entire battery system to deliver or receive charge.
Most systems that deliver or receive charge from a battery system treat the battery system as a single source supply where voltage and current demands or impositions on the battery system are calculated for the performance of the system as a whole. Some systems monitor voltages at each battery and adjust the overall system voltage or current based on differences in voltage so as not to place excessive strain on any given battery. Voltage, however, is a very crude and inaccurate measure of a battery""s ability to deliver or receive charge and thus, provides only limited information with which to control the overall system, resulting in somewhat inefficient operation of the battery system.
Thus, there is a need for efficient management of energy flow to and from a battery system. More accurate control of load and charging current is needed to maximize energy efficiency.
The present invention addresses the above need by providing an apparatus, method, media and signal for controlling energy transfer between an energy bus and a system of batteries, in which a control signal generator operable to receive an extreme voltage representation representing a voltage of a battery exhibiting an extreme voltage among voltages of all batteries in the system, and a representation of a reference voltage derived from an operating parameter associated with the battery exhibiting the extreme voltage, is operable to produce a control signal for use in changing the amount of energy transfer between the energy bus and the battery system in response to the aforementioned representations. The control signal may be used by a load/charging device such as a motor/generator to control the flow of energy from and to the system of batteries.
Effectively, using the system and methods described above, the voltage of any given battery relative to the voltage of other batteries in the battery system determines whether or not a battery is selected for more careful analysis based on an operating parameter of that battery. This operating parameter may be used to determine a reference voltage which is used in conjunction with the voltage of the selected battery to produce a control signal such as a current change signal and/or a voltage change signal. Thus, a battery""s relative voltage performance is used to invoke an investigation of its operating conditions to determine how best to adjust the charge or discharge current or more generally to adjust the energy flowing to or from the battery system as a whole.
In accordance with one aspect of the invention, there is provided an apparatus for controlling energy transfer between an energy bus and a system of batteries. The apparatus includes an accessor operable to access an extreme voltage representation representing a voltage of a battery exhibiting an extreme voltage among voltages of all batteries in the system and operable to access a representation of a reference voltage derived from an operating parameter associated with the battery exhibiting the extreme voltage. The apparatus also includes a control signal generator in communication with the accessor and operable to produce a control signal for use in changing the amount of energy transfer between the energy bus and the system in response to the representation of a reference voltage and the representation of the voltage extremity.
The apparatus may include a voltage extremity processor operable to produce the representation of the voltage extremity and may include memory accessible by the voltage extremity processor, for receiving and storing representations of voltages of batteries in the system. The voltage extremity processor may be configured to determine which of the representations represents the extreme voltage, and this may be done by employing a sorter to sort the representations of voltages.
The apparatus may further comprise a reference voltage processor operable to produce the representation of the reference voltage. This reference voltage processor may be operable to receive a representation of an operating parameter such as temperature of the battery exhibiting the extreme voltage. The reference voltage processor may have a look-up table interface operable to employ the temperature representation as an index to a look-up table relating reference voltages to temperature. The particular look-up table used may be selected as a function of state of charge of the battery having the extreme voltage. The look-up table interface may include an input operable to receive a representation of state of charge, for example, or the apparatus may include a state of charge processor operable to produce a representation of state of charge.
The look-up table interface may be able to employ the temperature representation as an index to a look-up table relating optimal charging voltages to temperature and/or a look-up table relating lowest permissible battery voltages to temperature, for example.
The apparatus may further comprise memory for receiving and storing a representation of voltage and a representation of temperature for each battery in the system and alternatively or in addition, the apparatus may include a device for producing the representation of voltage and the representation of temperature for each battery in the system.
The apparatus may employ an associator operable to associate respective voltage and temperature representations with corresponding batteries.
The apparatus may include a selector operable to select, as the temperature representation for use by the reference voltage processor, a temperature representation associated with a battery with which the extreme voltage is associated.
The control signal generator may have a difference processor operable to find a mathematical difference between the reference voltage and the extreme voltage and may be operable to produce a current change value indicative of a change in current available from the system of batteries and/or it may be operable to produce a voltage change value indicative of a desired change in voltage to be applied to the system of batteries. In addition, the control signal generator may be operable to produce a target bus voltage as a function of a previous target bus voltage and the voltage change value.
The apparatus may include an energy flow determiner operable to determine whether or not energy transfer is to the energy bus or to the battery system. The energy flow determiner may cooperate with the control signal generator or may be integrated therein, for example, to cause the control signal generator to produce a current change signal when energy is flowing to the bus and to produce a voltage change signal when energy is flowing to the battery system.
The apparatus may also include a bypass controller operable to produce a bypass activation signal for activating a bypass circuit on any battery having a voltage greater than a reference value, when there is no change in the direction of current flow through the battery system. The bypass controller may also produce a bypass circuit de-activation signal for de-activating a bypass circuit on any battery having an activated bypass circuit when there is a change in the direction of current flow in the system unless any battery has a voltage greater than the reference value.
In accordance with another aspect of the invention, there is provided a method of optimizing energy transfer between a system of storage batteries and an energy bus, the method comprising producing a control signal for use in changing the amount of energy transfer between the energy bus and the system of batteries in response to a representation of a reference voltage determined from an operating parameter of a battery exhibiting a voltage extremity and a representation of the voltage extremity.
In accordance with another aspect of the invention, there is provided a computer readable medium for providing codes for directing a processor circuit to control energy transfer between an energy bus and a system of batteries by producing a control signal for changing the amount of energy transfer between the energy bus and the system of batteries in response to a representation of a reference voltage determined from an operating parameter of a battery exhibiting a voltage extremity and a representation of the voltage extremity.
In accordance with another aspect of the invention, there is provided a signal comprising a segment providing codes for directing a processor circuit to control energy transfer between an energy bus and a system of batteries, the codes including codes for directing the processor circuit to produce a control signal for use in changing the amount of energy transfer between the energy bus and the system of batteries in response to a representation of a reference voltage determined from an operating parameter of a battery exhibiting a voltage extremity and a representation of such voltage extremity.